(a) Field of the Invention
The present invention relates to a novel silicon-containing polymer which is useful as a heat-resistant polymer, a burning-resistant polymer, a conductive polymer and a material for luminescent elements, non-linear elements as well as a method for preparing the silicon-containing polymer and a hardened product of the polymer.
(b) Description of the Prior Art
Recently, there have intensively and widely been conducted studies of heat-resistant polymers such as carbon-based polymers represented by polyimides; and silicon-based polymers such as silicone and polycarbosilane. The silicon-based polymers can molecularly been designed easily since they include bonds of high bonding energy such as Si--O and Si--C or those having high reactivity such as Si--Cl and Si--H. Nevertheless, there have only a few studies of heat-resistant silicon-containing polymers except for silicone. As examples of polycarbosilanes, silicon-containing polymers having structures represented by the following structural formula (6): ##STR2## (wherein R" represents a methyl or phenyl group; Ar represents a divalent aromatic group) have been synthesized in the presence of a catalyst such as a Pd catalyst. However, there have been limitations in the means available for the synthesis of these silicon-containing polymers having such structures and starting materials required for the polymerization thereof and therefore, only a few compounds have conventionally been synthesized (see, for instance, Robert J. P. Corriu et al., Journal of Polymer Science: Part C: Polymer Letters, 1990, 28, pp. 431-437). The inventors of this invention have taken note of such polymers which carry, in the main chain, ethynylene groups, aromatic groups and silylene groups and expected that these polymers exhibit high heat resistance and high resistance to burning. Since it would be assumed that physical properties of polymers largely differ from one another depending on the kinds of substituents thereof, the inventors have conducted various studies to develop further improved novel compounds. The inventors have made effort to develop, in particular, compounds having structures represented by the foregoing structural formula (6) in which either or both of the substituents R" on the silicon atom are hydrogen atoms since they can converted into other compounds exhibiting specific physical properties through, for instance, the crosslinking reaction of Si--H groups with ethynylene groups. However, it is difficult to synthesize these compounds according to the method disclosed in the aforementioned article of R. J. P. Corriu et al. because of the specific reactivity of the Si--H bond.
As examples of compounds having Si--H bonds include those synthesized by J. F. Harrod et al. in Canada, which are represented by the structural formula (6) wherein the substituents R" on the silicon atom represent a phenyl group and a hydrogen atom and the aromatic group Ar represents an m-phenylene group and which are prepared by subjecting phenylsilane and m-diethynylbenzene to dehydrogenation polycondensation in the presence of copper chloride and an amine compound as catalytic compounds (Hua Qin Liu and John F. Harrod, The Canadian Journal of Chemistry, Vol. 68, pp. 1100-1105). However, the compound was found to have structural defects in the main chain of the polymer in a high density, due to side reactions of ethynylene portions such as branching and/or crosslinking. These structural defects adversely affect various properties of the polymer such as the heat resistance, resistance to burning, solubility in a solvent and conductivity thereof. For this reason, the inventors of this invention have conducted studies to develop a novel method for the preparation of such a polymer.
The inventors of this invention have conducted various studies to develop a method for synthesizing a compound free of the foregoing structural defects and have already developed a method for preparing a polymer substantially free of the foregoing structural defects, which has a structure represented by the structural formula (6) wherein the substituents R" on the silicon atom represent a phenyl group and a hydrogen atom and the aromatic group Ar represents an m-phenylene group, the method comprising subjecting phenylsilane and m-diethynylbenzene to dehydrogenation polycondensation in the presence of a solid basic catalyst such as magnesia (Japanese Un-examined Patent Publication (hereunder referred to as "J. P. KOKAI") No. Hei 5-345825). In this method, however, the preparation of a polymer wherein two R" are both hydrogen atoms or one of them represents a hydrogen atom and the other represents a methyl group requires the use of gaseous monomers and this makes the preparation operations complicated.